The Ministry of Agriculture faced renewed calls yesterday to exterminate a growing colony of wild boars after a Dorset farmer was charged by a sow while strolling through a field.

David Puzey, of Mapperton, took refuge in his tractor to escape the sow, which turned on him after he stumbled across her five piglets.

The incident was the latest in a series of isolated attacks by wild boars, which are also blamed for wrecking crops and fences, preying on livestock and spreading disease. The ministry has commissioned a study of their numbers in an effort to determine the extent of the problem.

Hunted to extinction by the late 17th century, boars - prized since ancient times for the succulence of their flesh - are once again roaming Britain's woods and forests.

These new herds originate in the 40 or so farms that have sprung up in the past decade to capitalise on the growing taste for exotic meats. Boars escaped from captivity are thought to have bred with feral pigs and even with free-range commercial animals.

Estimates of their numbers vary. The National Farmers Union, which is demanding a concerted cull, says there may be several hundred. Others suggest just a few dozen.

What seems certain is that the biggest concentration is in the Kent/East Sussex border area, where several pairs escaped during the hurricane of 1987. Boars have also been spotted in the West Country, Scotland and Humberside.

While some conservationists welcome the return of a native species, for mainstream farmers they represent a pest. With their powerful snouts, they bulldoze through fences and plough up fields of crops. Earlier this year, a Kent farmer lost six lambs in one night.

"Our worry is that there is an expanding population establishing itself in different parts of the country," said Dafydd Owen, acting pigs adviser for the NFU. "They breed at an alarming rate and have no natural predators."

The danger to humans is less acute. Naturally shy, wild boars are unlikely to attack except during the rutting season or when protecting young. Once roused, however, they can be dangerous. They weigh up to 300lbs, move fast and have razor-sharp tusks. Cars have been badly damaged in collisions.

Dr Derek Booth, consultant to the British Wild Boar Association, pointed out that most European countries retain large populations of native boars. In France, hunters pay a hefty licence fee, some of which is channelled to farmers to enable them to pay for fences.

Tony Gent, vertebrate ecologist at English Nature, said the return of the wild boar had benefits from the conservation perspective. "In confined areas, they wipe out bluebells," he said. "But in digging up the ground, they can encourage a wider variety of flora."

With so little of their woodland habitat left, it is unlikely that a large population could thrive in Britain. "It's a sad fact, but wild boars are incompatible with modern life," said Dr Booth.

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